U.S. Pat. No. 4,245,165 discloses an analog programming device that is more difficult to program than the present invention. The reference requires thin gate oxides that allow electrons to tunnel in and out a floating gate. This is not compatible with most silicon wafer processes used for signal processing and logic, such as CMOS (complimentary metal oxide semiconductor). The high voltages required for programming cannot be selectively switched to control multiple adjustments without CMOS-process-incompatible high voltage logic. On the other hand, the programmable voltage offset circuit of the present invention can be made using CMOS and can be fabricated on the same chip as the circuit it controls.
This reference further differs from the present invention in that: (1) It uses analog, not digital, components; therefore, it is subject to drifting, is hard to program accurately, and is not readily reproducible. (2) The programming is not readily reversible. (3) No two-step programming is disclosed. The present invention uses initial temporary iterative latch memory programming followed by quasi-permanent nonvolatile memory programming.
U.S. Pat. No. 4,573,144 discloses a means for selecting multiple programming elements, in which an EPROM (erasable programmable read only memory) is programmed by placing a control voltage at the EPROM output via a FET (field effect transistor). This reference differs from the present invention in that:
(1) It does not disclose a two step programming process, whereas the present invention features initial iterative temporary programming followed by quasi-permanent nonvolatile memory programming. (2) The programmable element has fixed gates as well as a floating gate. This two-level gate structure is more complex and expensive than that of the EPROM's used in the present invention. (3) The reference inhibits avalanching by using leakage current, whereas the present invention inhibits avalanching by affirmatively placing a CMOS control signal of zero volts or 5 volts at the output of the EPROM.
U.S. Pat. No. 3,721,838 discloses a specialized programmable device for replacing defective elements in a monolithic device.
U.S. Pat. No. 4,050,030 discloses a specialized circuit for reducing temperature sensitivity in a differential amplifier, wherein the offset adjustment is controlled by external resistors.
U.S. Pat. No. 4,412,241 discloses an extension of a fusible link, in which the programming is irreversible and requires large currents. The reproducibility and reliability of this programming technique are below par. IBM Technical Disclosure Bulletin Volume 19, No. 8, January 1977, pages 3089-3090 also discloses a fusible link device.